Process for the detection and measurement of ionizing radiation by the use of radiation-degradeable material

ABSTRACT

Radiation-degradeable film, a portion of which has been irradiated, is treated initially with a basic solution, containing a chemical reagent which swells the material constituting the film, making it possible for the basic solution to attack the radiation degraded parts more deeply. Also, in a further operation the film may be treated with a solvent which dissolves surface roughness formed during the initial treatment so that the nondegraded parts recover their initial transparency while the more deeply attacked degraded parts remain visible. This method lends itself to automatic dosimetry in which the optical densities of irradiated and nonirradiated portions of the material are compared.

United States Patent Inventor Jean-Paul Lucien Goulin Vincennes, France Appl. No. 799,878

Filed Feb. 17, 1969 Patented Sept. 14, 1971 Assignee Eastman Kodak Company Rochester, N.Y.

Priority Mar. 5, 1968 France 142344/68 PROCESS FOR THE DETECTION AND MEASUREMENT OF IONIZING RADIATION BY THE USE OF RADIATION-DEGRADEABLE MATERIAL [56] References Cited UNITED STATES PATENTS 3,415,993 12/1968 Fleischer et al 250/83 3,493,751 2/1970 Davies et al. 250/83 CD Primary ExaminerArchie R. Brochelt Attorneys-William H. .l. Kline, Robert F. Crocker and Morton A. Polster ABSTRACT: Radiation-degradeable film, a portion of which has been irradiated, is treated initially with a basic solution, containing a chemical reagent which swells the material constituting the film, making it possible for the basic solution to attack the radiation degraded parts more deeply, Also, in a further operation the film may be treated with a solvent which dissolves surface roughness formed during the initial treatment so that the nondegraded parts recover their initial transparency while the more deeply attacked degraded parts remain visible. This method lends itself to automatic dosimetry in which the optical densities of irradiated and nonirradiated portions of the material are compared.

PATENTED SEP 1 4191:

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AA Fla 3 II I25 I I I I I I0 20 50 I00 200 JEAN-PAUL LUCIE/V GOULl/V INVENTOR.

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A TTOR/VE Y PROCESS FOR THE DETECTION AND MEASUREMENT OF IONIZING RADIATION BY THE USE OF RADIATION- DEGRADEABLE MATERIAL The present invention relates to the detection of ionizing radiation and to the recording of the tracks formed by such ionizing radiation in a radiation-degradeable material and, more particularly, to the treatment of such material to enhance the visible contrast between its irradiated and nonirradiated portions.

It is known that cellulose nitrate, as well as various other polymer and nonpolymer materials, e.g., certain micas, undergo a degradation when irradiated with ionizing particles, alpha particles, recoil protons and fission products, while remaining substantially insensitive to electromagnetic rays (light, ultraviolet, x and gamma rays) and to beta radiation. It is also known that chemical reagents, such as strongly basic aqueous solutions, attack the degraded parts and nondegraded parts of such irradiated material differently. Reference may be made, regarding this subject, to the article by R. L. Fleischer and his collaborators: Physical Review (5A), 133, p. A-1443- 1449 (Mar. 2, 1964).

According to this prior art method for the detection of radiation, cellulose nitrate is exposed to and selectively degraded by ionizing irradiation, and then attacked in the degraded parts by a warm basic solution. More particularly, a portion of a cellulose nitrate film in the form of a self-supporting sheet or a layer which is deposited on a sheet of inert, transparent support material, is irradiated with the radiation under study. Subsequently, the film is treated with a 6.5 N potassium hydroxide solution, at 55 C., which produces a marked depolishing of the degraded parts. By examining the film with effectively collimated transmitted light, it is possible to count the particle tracks. Nevertheless, the counting operation is long and fastidious in the cases where it is desired to effect dosimetry or measuring. In addition, the basic solutions used for revealing the particle tracks, also cause a certain depolishing of the nondegraded parts, thereby diminishing the transparency of these nondegraded areas as well.

It is an object of the invention to provide a simple method for treating radiation damaged materials which eliminates these disadvantages.

It is a further object to provide such a radiation detection process which replaces difficult and laborious track-counting procedures with simple photometric measurements, which are much faster and far easier for the operator.

These and other features of the invention will be described with reference to the accompanying drawings, in which:

FIGS. 1, 2, and 3 are graphic representations of the data of tables I, II, and III below, illustrating the increased efiectiveness of the embodiments of the invention, relative to the prior Initially, it should be noted that, as different from prior art counting techniques, the measuring technique proposed herein utilizes diffusion measurement of irradiated materials which does not differentiate between actual particle tracks and accidental depolishing. Therefore, in the process disclosed herein, it is important that the nondegraded parts remain substantially transparent.

According to the invention herein, it has been found that radiation-degradeable film, a portion of which has been exposed to radiation, may be treated initially with a basic alkaline metal solution, advantageously containing an agent such as an alkaline metal halide or alkaline metal thiocyanate that swells the material constituting the film, making it possible for the basic solution to attack the radiation-degraded parts more deeply. However, the basic solution still produces a general depolishing of the entire surface of the film. Therefore, the method herein includes a further operation, done under similar conditions, in which the film is treated in a different basic solution containing an agent e.g., ethyleneglycol, that dissolves cellulose nitrate. The film is thus polished by action of the ethylene'glycol, dissolving the small surface roughness formed over the entire surface during the initial treatment so that the nondegraded parts, in both the irradiated and nonirradiated portions, recover their initial transparency while the more deeply attacked degraded parts remain visible.

Thus, when viewed with effectively collimated light, it is possible to differentiate the light diffusion caused by the damaged and undamaged parts. This differentiation is of sufficient contrast so that it may be studied photometrically. The density of a continuous background (on the portion of the film protected from irradiation) is compared with the average density of the irradiated portion to give a measurement of the irradiation. Therefore, the difficult and lengthy counting of the particle tracks is replaced by two optical density measurements, similar to sensitometric measurements in photography. These measurements may be easily done by an automatic device. The invention thus provides an important improvement in the measurement of ionizing radiation.

On material that is capable of suitable degradation in the carrying out of the invention is cellulose nitrate. With this material, one obtains a highly improved sensitivity in comparison with that produced by the prior art treatment which uses only a single basic solution. The treatment using two solutions, according to the invention, makes possible the utilization of cellulose nitrate having addenda making that polymer particularly sensitive to ionizing radiation. It is thus now possible to use extremely sensitive cellulose nitrate layers having a high content of plasticizing camphor, even though such layers have been heretofore practically unusable with the prior art (one solution) treatment because of the general depolishing which the polymeric surface undergoes in the course of this treatment. For example, an extremely sensitive cellulose nitrate film, useful with the subject invention, can be prepared by casting a collodion made up of 20 parts, in a mass, of cellulose nitrate, containing approximately 3/100 to approximately 20/100 of camphor, in 80 parts of a solvent mixture comprising, for example, four parts of ethanol and one part of acetone.

Although cellulose nitrate is the preferred material for the method disclosed herein, special attention is called to the fact that cellulose nitrate may be replaced by other polymer materials. It is possible to use, in particular, the various cellulose acetates, cellulose acetate-nitrate, cellulose acetatepropionate cellulose acetate-butyrate, and certain polyesters such as poly(ethyleneglycol terephthalate), etc. It is possible to use these various polymers in the form of a film, either as a sheet sufficiently thick so that it can be handled, or as a layer deposited on a sheet of inert, transparent support material. Of course, plasticizers and/or other addenda may be added to the polymeric material to improve its qualities (e.g., the addition of camphor to cellulose nitrate, as indicated above).

In the case of cellulose nitrate films, the following two treatments will be used advantageously:

Attacking Treatment: place the film or layer, for 20 minutes, in the following solution which is heated to 75 C.:

Caustic potash...50 g. Potassium thiocyanate (Swelling the cellulose nitrate,

without dissolving it)...300 g.

Water...650 g.

Repolishing Treatment: place the film or layer, for 5 minutes,

' in the following solution which is heated to 75 C.:

Caustic potash... g.

Ethyleneglycol (dissolving the cellulose nitrate without swelling it)... 500g.

Water...400 g. I

The potassium thiocyanate may be replaced by an alkaline metal halide, particularly by potassium chloride. The ethylene glycol may be replaced by ethanol, in a smaller amount.

While caustic soda solutions may be used herein, generally, the caustic potash solutions are preferred.

It should be noted that the prior art single-solution method is improved according to the invention herein by the use of a swelling agent. However, the preferred embodiment of the process herein is characterized by the successive use of two different chemical solutions. The second of these solutions does not swell the film but repolishes it by superficial dissolution, which renders the degraded parts particularly visible and makes it possible to measure the degradation by the difference of light diffusion between the irradiated and the nonirradiated areas.

According to the preferred form of the invention, the process comprises the following series of operations: (1) the ionizing particles are received on a portion of a cellulose nitrate film plasticized by camphor, devoid of any support, approximately 50 p. to 400 p, thick; (2) this film is attacked by a caustic potash aqueous solution, containing potassium thiocyanate, having a potassium hydroxide content between 1.0 N and 10 N, between 20 and 100 C., for a period of time that is sufficient to depolish the entire surface of the film; (3) the at tacked film is then treated with a repolishing solution, likewise containing caustic potash and having a potassium hydroxide content between 1.0 N and 10 N, and also containing a solvent for the cellulose nitrate, such as ethyleneglycol, between 20 and 100 C., for a period of time that is necessary to repolish the nondegraded parts by dissolution of the surface, but insufficient to repolish the degraded parts by dissolution of the surface; and then (4) after washing with water and drying, the film is examined photometrically in collimated light, and the difference between the densities of the nonirradiated and of the irradiated portions, which have been measured by means of diffusion, is calculated.

The following examples, tabulated in each of the respective Tables set out below, illustrate the invention with reference being made to the attached drawing wherein the various figures are graphs of the tabulated information. On each of the graphs, time (t) is expressed logarithmically in seconds, while differences in optical density (A) between the irradiated and the nonirradiated areas of each sample are expressed linearly as arbitrary quantities.

EXAMPLE 1 1.35

A 200p. thick film, exempt from any support, is prepared by flowing a collodion made up of 20/100 cellulose nitrate, to which have been added 8/100 of camphor, and 80/100 of a mixture of four parts of ethanol and one part of acetone. This film is cut into 32 fragments; four fragments are kept as test samples, and seven groups of four fragments each are irradiated, respectively, for 2 seconds, seconds, 10 seconds, seconds, 50 seconds, 100 seconds and 200 seconds, under masks provided with a 17 mm. X 12 mm. opening, with a 1.35 .Ci alpha radiation, emitted by the radioactive element Am, the source being placed at a distance of 16 mm. from the films.

Each of the series comprising a nonirradiated test sample and seven fragments that have received increasing irradiation, is treated separately in the following manner:

Series A: known treatment with a 6.25 N solution of caustic soda, at 55 C. for 50 minutes.

Series B: treatment with a potash solution containing 60 g. of potassium hydroxide per liter, at 75 C., for minutes.

Series C: treatment similar to that of series B, the potash solution containing potassium thiocyanate, swelling the cellulose nitrate without dissolving it, the formula being as follows: Solution 1: Caustic potash...60 g.

Potassium thiocyanate...400 g.

Water...enough to make up...1,000 ml.

Series D: treatment according to the invention comprising the treatment of the above Series C, followed by a treatment, for 3 minutes, at 75 C., in the following solution, containing a solvent for the cellulose nitrate:

Solution ll: Caustic Potash...80 g.

Ethyleneglycol...600 g.

Water...enough to make up... l ,000 ml.

The optical density of the various samples is measured by means of a Baldwin densitometer, and is designated by the letter d in the tables below, a d value of 2.50 indicating reflection from a black glass. Each irradiated sample is characterized by the density of its nonirradiated, substantially transparent part (indicated in the Tables as the value ofd at 0" seconds of irradiation) and the difference (A in the tables) between the density of the irradiated and the nonirradiated areas of the sample.

The results obtained are listed in table 1 and applied to the graph of FIG. 1. They show the great superiority of the 30 treatment according to the preferred embodiment of the invention (series D) over the one-solution, prior art treatment (series A).

TABLE L-OELLULOSE NITRATE CONTAINING 8/100 OF CAMPHOR Treatment;

d A d A d A d A Duration of irradiation (in seconds):

0 1.61 0 2. 03 0 2.02 0 2.11) 0 1. 98 0. 04 2. 16 0. 03 2.03 0 1. 01 0.11 2. 0-1 0. 15 1. 61 0 2.00 0. 03 1. 75 0.27 1. 8O 0. 39 1. 55 0.06 1. 93 0. 10 1. 53 0. 40 1. 54 '0. 65 1. 45 0.16 1. 73 0.30 1. 29 0. 73 1. 26 0.93 1. 30 0.30 1. 51 0. 52 1.03 0. 99 0. JG 1. 23 1. 0i) 0. 52 1. 26 0. 77 0. 75 1. 27 0. 71 1. 45

EXAMPLE 2 Tests are made similar to those of example 1, but cellulose nitrate containing 15/ 100 of camphor is used and a mixture of seven parts of alcohol and three parts of ether (in volume) is used as a solvent.

The obtained results are shown in table I1 and applied to the graph of F IG. 2. These results show that the treatment carried out in two operations according to the invention improves the results obtained with cellulose nitrate that is plasticized with 15/100 camphor, much more than it improves the results obtained with only 8/100 of camphor. This is evident from the comparison between tests C, and D,, the letters 8,, and C, and D, referring to samples prepared in the same manner as in Series B, C and D in example 1.

TABLE II.CELLULOSE NIIRATE CONTAINING 15/100, OF CAMPHOR EXAMPLE 3 Examples 1 and 2 show the improvement attained by the double treatment according to the preferred form of the invention when the first treatment solution contains an agent that swells the cellulose nitrate. The following example, in connection with cellulose nitrate containing 15/100 of camphor, shows that the double treatment also improves the results when the first solution is a simple caustic potash solution. The irradiation conditions are those of the preceding examples and the treatments are the following: Treatment E: g. of caustic potash per liter, for 45 minutes at 75 C. Treatment F: the above Treatment E, followed by a 3-minute treatment at 75 C. in the above solution ll and shown graphically in FIG. 3.

The results obtained are shown in table 111.

The new process for the detection and measurement of ionizing particles, according to the invention, can be used advantageously in numerous cases. It offers the advantage of being relatively insensitive to light, X-rays gamma rays and to beta particles. Therefore, even in radioactive environments, the invention herein makes possible autoradiography of emitters of alpha particles and other ionizing particles, as well as the dosimetry of fast neutrons, such neutrography being by means of an energy-transforming emitter of ionizing particles.

EXAMPLE 4 Onto a polyethylene terephthalate film, cellulose nitrate varnish is coated, containing 8 percent camphor, to obtain a 8 p. dry coat. This film is cut into 21 fragments; three fragments are kept as control samples and six groups of three fragments each are irradiated, respectively for 60 seconds, 120 seconds, 300 seconds, 900 seconds, 1800 seconds and 3200 seconds in the same conditions as in example 1.

Each of the series comprising a nonirradiated control sample and six fragments that have received increasing irradiation is treated separately in the following manner:

SERIES A: known treatment with a 6.5 N solution of caustic soda, at 55 C. for 6 minutes.

SERIES B: the same treatment as for series A 1 minute treatment with solution II of example 1.

SERIES C: treatment with solution I of example I at 75 C. during 3 minutes.

The results, indicated in table IV, show that series C and especially series B give results better than series A.

TABLE IV.CELLULOSE NIIRATE ON POLY- E'IHYLENE TEREPHTHALAIE SHEET A B C d A d A d A This table, and particularly the differences A, show that the results obtained with the treatment of series C and especially of series B are much better than those obtained with the treatment of series A.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

lclaim:

1. In a process for the detection and measurement of ionizing-particlc radiation, said process including the steps of (a) exposing to such radiation a material which undergoes degradation in its presence and (b) the treatment of said material in a strongly basic aqueous solution which preferentially attacks those parts of the material which are degraded by said radiation, the improvement wherein said solution further comprises a chemical reagent which swells said material whereby said degraded parts are attacked more deeply.

2. The process according to claim 1 wherein said swelling reagent comprises an alkaline metal halide.

3. The process according to claim 1 wherein said swelling reagent comprises an alkaline metal thiocyanate.

4. The process according to claim I wherein said radiationdegradeable material is selected from the group consisting of cellulose nitrate, cellulose acetate, cellulose acetate-nitrate, cellulose acetate-propionate, cellulose acetate-butyrate, and poly(ethyleneglycol terephthalate).

5. The process according to claim I wherein said strongly basic aqueous solution comprises potassium hydroxide.

6. The process according to claim 1 wherein only a portion of said material is exposed to said radiation and wherein said process comprises the additional steps of:

determining the optical density of the unexposed portion of said material,

determining the optical density of the exposed portion of said material, and

comparing said density determinations to provide a measurement of said ionizing-particle radiation.

7. In a process for detecting and measuring ionizing-particle radiation, said process including the steps of (a) exposing to such radiation a material which undergoes degradation in its presence and (b) the treatment of said material in a strongly basic aqueous solution which preferentially attacks those parts of the material which are degraded by said radiation, said solution also producing a general depolishing of the nondegraded parts of said material, the improvement wherein said process includes the further step of:

treating said material in a second solution comprising a solvent which repolishes said depolished nondegraded parts.

8. The process according to claim 7 wherein said solvent comprises ethyleneglycol.

9. The process according to claim 7 wherein said radiationdegradeable material is selected from the group consisting of cellulose nitrate, cellulose acetate, cellulose acetate-nitrate, cellulose acetate-propionate, cellulose acetate-butyrate, and poly(ethyleneglycol terephthalate).

10. The process according to claim 7 wherein said strongly basic aqueous solution comprises potassium hydroxide.

11. The process according to claim 7 wherein only a portion of said material is exposed to said radiation and wherein said process comprises the additional steps of:

determining the optical density of the unexposed portion of said material,

determining the optical density of the exposed portion of said material, and

comparing said density determinations to provide a measurement of said ionizing-particle radiation.

12. The process according to claim 7 wherein said basic aqueous solution further comprises a chemical reagent which swells said material whereby said degraded parts are attacked more deeply.

13. The process according to claim 12 wherein said swelling reagent comprises an alkaline metal halide.

14 The process according to claim 12 wherein said swelling reagent comprises an alkaline metal thiocyanate.

15. The process according to claim 7 wherein said radiation-degradeable material is cellulose nitrate substantially free from stabilizing agents and plasticized with camphor, said strongly basic aqueous solution comprises a swelling reagent which is selected from the group consisting of alkaline metal thiocyanates and halides, and said second solution comprises a solvent selected from the group consisting of ethanol and ethyleneglycol.

16. The process according to claim 15 wherein said cellulose nitrate comprises a sheet having a thickness of Sop-400p. and containing approximately 3/ I00 to approximately 20/ I00 of camphor.

17. The process according to claim 16 wherein the treatment of said cellulose nitrate sheet comprises treating it at a temperature of 30-90 C. for 5 minutes to 60 minutes in the following solution 56 g. to 200 g.

100 g. to 400 g.

mn.-l 5 mn. in the following solution Potassium hydroxide Ethyleneglycol Water 56 g. to 200 g. 200 g to 600 g. 

2. The process according to claim 1 wherein said swelling reagent comprises an alkaline metal halide.
 3. The process according to claim 1 wherein said swelling reagent comprises an alkaline metal thiocyanate.
 4. The process according to claim 1 wherein said radiation-degradeable material is selected from the group consisting of cellulose nitrate, cellulose acetate, cellulose acetate-nitrate, cellulose acetate-propionate, cellulose acetate-butyrate, and poly(ethyleneglycol terephthalate).
 5. The process according to claim 1 wherein said strongly basic aqueous solution comprises potassium hydroxide.
 6. The process according to claim 1 wherein only a portion of said material is exposed to said radiation and wherein said process comprises the additional steps of: determining the optical density of the unexposed portion of said material, determining the optical density of the exposed portion of said material, and comparing said density determinations to provide a measurement of said ionizing-particle radiation.
 7. In a process for detecting and measuring ionizing-particle radiation, said process including the steps of (a) exposing to such radiation a material which undergoes degradation in its presence and (b) the treatment of said material in a strongly basic aqueous solution which preferentially attacks those parts of the material which are degraded by said radiation, said solution also producing a general depolishing of the nondegraded parts of said material, the improvement wherein said process includes the further step of: treating said material in a second solution comprising a solvent which repolishes said depolished nondegraded parts.
 8. The process according to claim 7 wherein said solvent comprises ethyleneglycol.
 9. The process according to claim 7 wherein said radiation-degradeable material is selected from the group consisting of cellulose nitrate, cellulose acetate, cellulose acetate-nitrate, cellulose acetate-propionate, cellulose acetate-butyrate, and poly(ethyleneglycol terephthalate).
 10. The process according to claim 7 wherein said strongly basic aqueous solution comprises potassium hydroxide.
 11. The process according to claim 7 wherein only a portion of said material is exposed to said radiation and wherein said process comprises the additional steps of: determining the optical density of the unexposed portion of said material, determining the optical density of the exposed portion of said material, and comparing said density determinations to provide a measurement of said ionizing-particle radiation.
 12. The process according to claim 7 wherein said basic aqueous solution further comprises a chemical reagent which swells said material whereby said degraded parts are attacked more deeply.
 13. The process according to claim 12 wherein said swelling reagent comprises an alkaline metal halide. 14 The process according to claim 12 wherein said swelling reagent comprises an alkaline metal thiocyanate.
 15. The process according to claim 7 wherein said radiation-degradeable material is cellulose nitrate substantially free from stabilizing agents and plasticized with camphor, said strongly basic aqueous solution comprises a swelling reagent which is selected from the group consisting of alkaline metal thiocyanates and halides, and said second solution comprises a solvent selected from the group consisting of ethanol and ethyleneglycol.
 16. The process according to claim 15 wherein said cellulose nitrate comprises a sheet having a thickness of 50 Mu -400 Mu and containing approximately 3/ 100 to approximately 20/ 100 of camphor.
 17. The process according to claim 16 wherein the treatment of said cellulose nitrate sheet comprises treating it at a temperature of 30* -90* C. for 5 minutes to 60 minutes in the following solution Potassium hydroxide 56 g. to 200 g. Potassium thiocyanate 100 g. to 400 g. Water 650 cc. and afterwards treating it at a temperature of 30*-90* C. for 1 mn.- 15 mn. in the following solution Potassium hydroxide 56 g. to 200 g. Ethyleneglycol 200 g. to 600 g. Water 400 cc. 